General purpose polystyrene (GPPS) is a polymer made from styrene, a vinyl aromatic monomer that can be produced from aromatic hydrocarbons, for example those derived from petroleum. GPPS is useful in a variety of applications, such as casing for appliances, molded into toys or utensils, or expanded to create foamed styrene. In most cases, GPPS is a hard and brittle plastic, however, the use of comonomers may alter its physical properties. Ionic comonomers, for example, may alter the properties of a polymer, such as melt flow rate, melt strength, polydispersity, and glass transition temperature.
Metal acrylates are an example of ionic comonomers that can be used to create a polystyrene branched ionomer. Zinc dimethacrylate (ZnDMA), for instance, is well known in the art as useful ionic comonomer for polystyrene production. Several drawbacks are associated with the use of prepared ZnDMA. ZnDMA can be expensive. Particles of ZnDMA powder tend to be less than 10 microns in diameter, causing inhalation hazards during transport to the reaction vessel due to dust. Further, ZnDMA does not easily dissolve into styrene. Feeding slurries of pre-formed ZnDMA comonomer to the reactor can be difficult; the ZnDMA may not suspend well and the consistency in feed concentration may be questionable. Swings in melt index can occur. In the reaction vessel, sticking of the methacrylate particles to the vessel surfaces can occur during mixing due to the static charge build-up on the surface of these polar compounds, resulting in gel formation and reactor fouling. Other metal acrylates can also have problems similar to those of ZnDMA when used as ionic comonomers for polystyrene.
Varying parameters such as reaction conditions, type and/or quantities of comonomer used may allow for the production of styrenic copolymer compositions tailored to meet the needs of a wide-range of end-use applications. Thus, an ongoing need exists for compositions and methodologies for the production of styrenic copolymers having improved properties.